Plasma processing apparatus and method for releasing sample

ABSTRACT

The invention provides a plasma processing apparatus which includes a processing chamber, a radio frequency power source to supply a radio frequency power for plasma generation, a sample stage equipped with an electrostatic chuck electrode of a sample, a DC power source to apply a DC voltage to the electrode, and a control unit to change the DC voltage from a predetermined value to almost 0 V when a predetermined time elapses since the supplying of the radio frequency power is stopped. The predetermined value is a predetermined value indicating that a potential of the sample when the DC voltage is almost 0 V becomes almost 0 V. The predetermined time is a time defined on the basis of a time when charged particles generated by the plasma processing disappear or a time when an afterglow discharge disappears.

CLAIM OF PRIORITY

The present application claims priority from Japanese patent applicationJP 2016-152424 filed on Aug. 3, 2016, the content of which is herebyincorporated by reference into this application.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention relates to a plasma processing apparatus and amethod for releasing a sample from a sample stage.

2. Description of the Related Art

As one of plasma processing methods of manufacturing a semiconductor,there is a plasma etching. In the plasma etching, a sample (wafer) isplaced on a sample stage in a processing chamber, and exposed to plasma.At this time, a specific stacked film is selectively removed from thewafer by adjusting various processing conditions such as a gas chemistryto be introduced into the processing chamber and a radio frequency powerto be applied to the wafer, so that a fine circuit pattern is formed onthe wafer.

In such a plasma etching, there is a need to prevent a wafer deviationduring the processing and to adjust a wafer temperature. Therefore, thewafer is electrostatically adsorbed onto the sample stage typicallyusing an electrostatic chuck electrode. The electrostatic adsorption ofthe wafer is released after the plasma etching ends. The wafer isreleased from the sample stage using a releasing mechanism which pushesup the wafer upward the sample stage, and then carried out of theprocessing chamber.

In the wafer adsorption using the electrostatic chuck electrode, thewafer is adsorbed by an electrostatic force generated in a dielectricfilm between the electrode and the wafer by applying a voltage to anelectrode. Therefore, the adsorption can be released by turning off thevoltage applied to the electrostatic chuck electrode. However, at thistime, if the dielectric film and the wafer are insufficientlyneutralized, charges are left. Therefore, an adsorption force may beapplied onto the wafer even after the voltage applied to the electrodeis turned off.

Since such a residual adsorption force is generated, a position of thewafer may be deviated when the wafer is released from the sample stage,or the wafer may be damaged by a force applied to the wafer when beingreleased. The wafer deviation may lead to a transport error when thewafer is carried out. In some cases, a process of manufacturing productsmay be stopped. The damage of the wafer causes a loss in the waferitself, and also requires a time for removing the damaged wafer from anapparatus to recover the apparatus. Either case has a strong possibilityto cause an adverse influence on productivity of the process ofmanufacturing the wafers. Therefore, the residual adsorption forcecaused by the neutralization is necessarily lowered in order to reducethe above risks. In addition, as a neutralization method for reducingthe residual adsorption force, the following methods have been known sofar.

JP 2004-47511 A discloses a neutralization processing method forreleasing, from a dielectric body, an adsorbed object which is placed onthe dielectric body equipped with an electrode and adsorbed to thedielectric body by an electrostatic force generated when a predeterminedpolarity of DC voltage is applied to the electrode. The method includesstopping the DC voltage from being applied to the electrode, exposingplasma for neutralizing the adsorbed object, and applying the electrodewith a DC voltage having the same polarity as that of a self-biasvoltage which is generated in the adsorbed object by the exposure of theplasma.

SUMMARY OF THE INVENTION

JP 2004-47511 A describes stopping of the voltage application to theelectrostatic chuck electrode and stopping of the voltage applicationsimultaneously with stopping of the applying of the radio frequencyvoltage for generating the plasma. However, at the time when the plasmaprocessing ends, the charged particles in the plasma are left in a spaceeven after the incident power of the radio frequency power forgenerating the plasma is stopped. As described in a neutralizationmethod disclosed in JP 2004-47511 A, when the voltage applied to theelectrostatic chuck electrode is set to 0 V at the same time when theplasma processing ends, the wafer has a potential by the residualcharged particles. A potential difference is caused again between thewafer and the electrode, and thus there is a concern that the residualadsorption force is generated.

In particular, in the case that the resistance value of the dielectricfilm between the wafer and the electrostatic chuck electrode issufficiently large, residual adsorption tends to remain for a long time.In other words, since the current flowing between the wafer and theelectrode with high resistive dielectric film, such as Coulomb typeelectrostatic chuck electrode, is significantly small, the residualadsorption force generated as described above is not released for a longtime.

Therefore, in order to avoid the above problems, the stopping of thevoltage application to the electrostatic chuck electrode may beperformed after the stopping of the application of the radio frequencyvoltage for generating the plasma. However, JP 2004-47511 A fails todescribe about a relation of a relative order between a timing ofstopping the voltage application to the electrostatic chuck electrodeand a timing of stopping the radio frequency voltage for generating theplasma.

Therefore, it can be said that JP 2004-47511 A has no considerationabout that the wafer is charged again by the charged particles left in avacuum processing chamber when the neutralization plasma processing endsafter the neutralization, and thus the residual adsorption force isgenerated by the charging.

The invention provides a plasma processing apparatus which can perform aneutralization processing in consideration of recharging of a wafercaused by the residual charged particles in the processing chamber aftera radio frequency power for generating the plasma is stopped, and amethod for releasing a sample from a sample stage in the neutralizationprocessing.

The invention provides a plasma processing apparatus which includes aprocessing chamber in which a sample is subjected to a plasmaprocessing, a radio frequency power source which supplies a radiofrequency power to generate plasma, a sample stage which includes anelectrode to electrostatically adsorb the sample and is used to placethe sample, a DC power source which applies a DC voltage to theelectrode, and a controller which changes the DC voltage from apredetermined value to almost 0 V when a predetermined time elapsessince the supplying of the radio frequency power is stopped. Thepredetermined value is a predetermined value indicating that a potentialof the sample when the DC voltage is almost 0 V becomes almost 0 V. Thepredetermined time is a time defined on the basis of a time when chargedparticles generated by the plasma processing disappear or a time when anafterglow discharge disappears.

In addition, the invention provides a method for releasing a sample froma sample stage, in which the sample is released from the sample stagewhere the sample is electrostatically adsorbed. In the method, a DCvoltage applied to an electrode for electrostatically adsorbing thesample to the sample stage is changed from a predetermined value toalmost 0 V after a predetermined time elapses since supplying a radiofrequency power to generate plasma is stopped. The predetermined valueis a predetermined value indicating that a potential of the sample whenthe DC voltage is almost 0 V becomes almost 0 V. The predetermined timeis a time defined on the basis of a time when charged particlesgenerated by the plasma processing disappear or a time when an afterglowdischarge disappears.

According to the invention, it is possible to perform a neutralizationprocessing in consideration of recharging of a wafer caused by theresidual charged particles in a processing chamber after a radiofrequency power for generating the plasma is stopped.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram schematically illustrating a configuration of avertical cross section of a plasma processing apparatus according to theinvention;

FIG. 2 is a diagram illustrating a potential difference between anelectrostatic chuck electrode and a wafer of a conventionalneutralization processing;

FIGS. 3A to 3D are a timing chart illustrating a neutralizationprocessing according to the invention;

FIG. 4 is a diagram illustrating an equivalent circuit obtained bymodeling variable DC power sources, electrostatic chuck electrodes, adielectric layer, and the wafer;

FIGS. 5A and 5B are graphs illustrating a measurement result of afloating potential; and

FIGS. 6A to 6E are a timing chart illustrating the neutralizationprocessing according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates a schematic configuration of a vertical cross sectionof a plasma processing apparatus in this embodiment. The plasmaprocessing apparatus of FIG. 1 is a plasma etching apparatus of anelectron cyclotron resonance (ECR) type. Hereinafter, the electroncyclotron resonance will be referred to as ECR.

The plasma processing apparatus which is the ECR-type plasma etchingapparatus of FIG. 1 performs an etching processing on a sample bygenerating plasma in a processing chamber 101 where a wafer (sample) 103is placed on a sample stage (a placing stage of a sample) 102 disposedin the processing chamber (vacuum processing chamber) 101.

The plasma processing apparatus includes solenoid coils 104 whichgenerate a static magnetic field in the processing chamber 101, amicrowave power source 105 which is a radio frequency power source, amicrowave oscillation source 106 (magnetron), a waveguide 107, and acontroller 115 which controls the etching processing. A magnetic fieldis formed in the processing chamber 101 by the solenoid coils 104. Themicrowave oscillated by the microwave oscillation source 106 caused bythe radio frequency power from the microwave power source 105 isintroduced to the processing chamber 101 through the waveguide 107. Themicrowave gives energy to the electrons by the ECR in the magnetic fieldformed by the solenoid coils 104. The electrons ionize gases suppliedfrom gas supply sources (not illustrated) to generate plasma.

A cooling gas is supplied to the backside of the wafer 103 to adjust thetemperature of the wafer 103 during the plasma processing. The wafer 103is electrostatically adsorbed onto the sample stage 102 by dipoleelectrostatic chuck electrodes 108 and 109 in order to prevent the wafer103 from being deviated due to the cooling gas. Herein, the dipoleelectrostatic chuck electrodes are electrostatic chuck electrodes whichelectrostatically adsorb the wafer 103 onto the sample stage 102 by DCvoltages applied to two electrodes. The electrostatic chuck electrodes108 and 109 of this embodiment are configured such that theelectrostatic chuck electrode (one electrode) 108 is disposed inside ona concentric circle, and the electrostatic chuck electrode 109 (theother electrode) is disposed outside.

As illustrated in FIG. 1, variable DC power sources 110 and 111(independent power sources) are respectively connected to theelectrostatic chuck electrodes 108 and 109. The variable DC power source110 is connected to the inside electrostatic chuck electrode 108, andthe variable DC power source 111 is connected to the outsideelectrostatic chuck electrode 109. A dielectric layer 112 is disposedbetween the electrostatic chuck electrodes 108 and 109 and the wafer103. Further, the electrostatic chuck electrodes 108 and 109 and thewafer 103 are electrically connected with a finite resistance value anda finite electrostatic capacitance. In this embodiment, it is assumedthat the resistance value of the dielectric layer is very large, and thewafer and the electrostatic chuck electrode are electrically connectedonly through the electrostatic capacitance.

In addition, a reverse-polarity voltage is applied to each of theelectrostatic chuck electrodes 108 and 109 by the variable DC powersources when the wafer is adsorbed onto the sample stage. For example, avoltage of +500 V is applied to the inside electrostatic chuck electrode108 by the variable DC power source 110, and a voltage of −500 V isapplied to the outside electrostatic chuck electrode 109 by the variableDC power source 111. However, in a case where there is no need to adsorbthe wafer, the same-polarity voltage may be applied to the electrostaticchuck electrodes 108 and 109.

When the same-polarity voltage is applied as described above, thepotential of the wafer can be controlled without performing theadsorption in a case where the plasma discharge is not performed. Forexample, the potential of the wafer can be made to have a positivepolarity by applying a voltage of +500 V to the inside electrostaticchuck electrode 108 by the variable DC power source 110 and by applyinga voltage of +500 V to the outside electrostatic chuck electrode 109 bythe variable DC power source 111.

The plasma processing apparatus includes passage holes 113 which areformed to pass through the sample stage, and pushing-up pins 114 whichare disposed in the passage holes to be vertically movable, as amechanism for releasing the wafer from the sample stage 102 after theetching processing ends and the electrostatic adsorption is released.After the electrostatic adsorption is released, the wafer is releasedfrom the sample stage 102 by pushing up the wafer toward the upper sideof the sample stage 102 using the pushing-up pins 114 which are a set ofreleasing mechanism. Then, the wafer raised by the pushing-up pins iscarried out of the processing chamber using a conveying mechanism (notillustrated).

Next, the problems in a potential difference between the electrostaticchuck electrode and the wafer at the time of the conventionalneutralization processing, and the process thereof will be describedusing a timing chart of a neutralization processing in the conventionalprocessing methods illustrated in FIG. 2. Herein, the neutralization isa process of releasing the electrostatically adsorbed wafer from thesample stage in order to carry the wafer 103 electrostatically adsorbedon the sample stage 102 from the processing chamber 101 after the plasmaprocessing (plasma etching) ends. Further, the description in theconventional processing method illustrated in FIG. 2 will be given usinga monopole electrostatic chuck electrode.

First, a microwave incident power is changed to generate the plasma forthe neutralization after the etching processing ends at T0 of FIG. 2.The changed microwave incident power is 400 W for example. At this time,the gas is desirably switched to generate the plasma for neutralizationat the same time. The plasma for neutralization is typically generatedusing an inert gas (for example, Ar and He). Next, a voltage applied tothe electrostatic chuck electrode at any time T1 during the plasma forneutralization is being generated is a voltage to cause the equal waferpotential in neutralization plasma using the variable DC power source.

In addition, in a case where a dielectric film between the wafer and theelectrostatic chuck electrode has a sufficiently large resistance value,the current rarely flows between the wafer and the electrostatic chuckelectrode, so that the potential of the wafer is determined not by thepotential variation of the electrostatic chuck electrode but only by theplasma state. Therefore, even when the potential is applied by thevariable DC power source as described above, the potential of the waferdoes not vary but equal to the potential of the electrostatic chuckelectrode at time T1. In this way, the potential difference between thewafer and the electrostatic chuck electrode disappears, so that anelectrostatic force working between the wafer and the electrostaticchuck electrode becomes small quickly.

Thereafter, the microwave power for generating the plasma is turned offwhen the voltage applied to the electrostatic chuck electrode becomes 0V. However, when the microwave power is turned off, the plasma does notinstantaneously disappear, but the charged particles in a plasma stateare left in the vacuum processing chamber even in a very short timeperiod. This phenomenon is an afterglow discharge after the microwavepower is turned off.

In a state where the charged particles are left in the vacuum processingchamber, the potential of the wafer is determined by the chargedparticles remaining in the vacuum processing chamber, the potential isgenerated in the wafer even when the voltage applied to theelectrostatic chuck electrode becomes 0 V at time T2, and a potentialdifference is caused again between the wafer and the electrostatic chuckelectrode at time T2 as illustrated in FIG. 2. An adsorption forcecaused by the potential difference is held for a long time in a casewhere the resistance of the dielectric film is large, and causes a waferdeviation or a wafer damage when the wafer is released from the samplestage by the pushing-up pins.

A method for releasing the wafer from the wafer stage according to theinvention to solve the above problem will be described using a timingchart illustrated in FIGS. 3A to 3D. FIG. 3A illustrates the incidentpower of the microwave, FIG. 3B illustrates the potential of theelectrostatic chuck electrodes, FIG. 3C illustrates the potential of thewafer, and FIG. 3D illustrates the potential difference between theelectrostatic chuck electrodes and the wafer. First, similarly to theconventional method for releasing the wafer, the neutralization plasmais generated at time T0 also in the invention, and the potentials of theinside electrostatic chuck electrode 108 and the outside electrostaticchuck electrode 109 at any time T1 during the neutralization plasma isgenerated are set to −ΔV with variable DC power sources. Further, theneutralization plasma is generated using an inert gas, and theneutralization in the invention may be performed using the same plasmaas that used at the time of the plasma processing (plasma etching)performed before the neutralization.

At this time, the potential difference between the wafer and theelectrode becomes “0” at time T1 as illustrated in FIG. 3D. Therefore,the electrostatic adsorption force working between the wafer and theelectrode disappears. Therefore, the radio frequency power (microwaveincident power) to generate the plasma for neutralization is blocked attime T2 in the invention. The charged particles left in the vacuumprocessing chamber disappear completely at time T3 elapsed by apredetermined time t after the radio frequency power is blocked. Thepotential of the wafer at that time is kept as it is during the plasmadischarge if the resistance value of the dielectric film is sufficientlylarge as illustrated in FIG. 3C. Herein, the predetermined time t hasbeen set to a time when the charged particles left in the vacuumprocessing chamber disappear, and may be set to a time taken until theafterglow discharge of the plasma for neutralization disappears.

In addition, since also the potentials of the electrostatic chuckelectrodes do not vary as illustrated in FIG. 3B, the potentialdifference between the wafer and the electrostatic chuck electrodes iskept to “0” as illustrated in FIG. 3D. There is no electrostaticadsorption force between the wafer and the electrode. Next, the DCvoltages are set to 0 V which is applied to the electrostatic chuckelectrodes at time T3 after the charged particles in the vacuumprocessing chamber disappear completely. At this time, the potentials ofthe electrostatic chuck electrodes vary, and the potential of the waferalso varies by the same amount as that of the potential of theelectrostatic chuck electrodes at almost the same time when thepotentials of the electrostatic chuck electrode vary. Such a change willbe described using a simplified equivalent circuit of the electriccircuit which includes the wafer after the plasma disappears, theelectrostatic chuck electrodes, the dielectric layer, and the variableDC power sources as illustrated in FIG. 4. Further, in the equivalentcircuit of FIG. 4, the resistance value of the dielectric film betweenthe wafer and the electrostatic chuck electrodes is assumed to besufficiently large, and only the electrostatic capacitance will beconsidered.

Ca and Cb of FIG. 4 are the electrostatic capacitance values of thedielectric layer, Qa and Qb are charges accumulated in the electrostaticcapacitance, and V1 and V2 are voltage values of the variable DC powersources. In addition, when the wafer potential is set to Vwaf, thefollowing Equation 1 is satisfied in the equivalent circuit illustratedin FIG. 4.

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 1} \right\rbrack & \; \\{{V_{waf} = {V_{1} + \frac{Q_{a}}{C_{a}}}}{{V_{1} + \frac{Q_{a}}{C_{a}}} = {V_{2} + \frac{Q_{b}}{C_{b}}}}} & {{Equation}\mspace{14mu} 1}\end{matrix}$

Further, since Qa=−Qb in this case, the wafer potential becomes thefollowing Equation 2 on an assumption of Qa=−Qb=Q.

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 2} \right\rbrack & \; \\{V_{waf} = {V_{1} + {\frac{C_{b}}{C_{a} + C_{b}}\left( {V_{2} - V_{1}} \right)}}} & {{Equation}\mspace{14mu} 2}\end{matrix}$

Herein, when Ca=Cb, the wafer potential becomes the following Equation3.

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 3} \right\rbrack & \; \\{V_{waf} = \frac{V_{1} + V_{2}}{2}} & {{Equation}\mspace{14mu} 3}\end{matrix}$

Therefore, when the potential of the electrostatic chuck electrodevaries to make V1 become V1+ΔV1 and V2 become V2+ΔV2, a variation amountΔVwaf of the wafer potential is obtained as the following Equation 4.

$\begin{matrix}\left\lbrack {{Expression}\mspace{14mu} 4} \right\rbrack & \; \\{{\Delta\; V_{waf}} = \frac{{\Delta\; V_{1}} + {\Delta\; V_{2}}}{2}} & {{Equation}\mspace{14mu} 4}\end{matrix}$

Therefore, when an average value of the potential of the insideelectrostatic chuck electrode 108 and the potential of the outsideelectrostatic chuck electrode 109 is shifted by ΔV, the wafer potentialis also shifted by ΔV. In addition, in a case where only the capacitanceis dominant, the variation of the wafer potential occurs immediatelyafter the changes of electrostatic chuck electrodes potentials.

As described above, since the potentials of the electrostatic chuckelectrodes and the potential of the wafer vary by the same amount at thesame timing at time T3, the potential difference between the wafer andthe electrostatic chuck electrodes is kept to be “0” at time T3 asillustrated in FIG. 3D. In other words, the potential of theelectrostatic chuck electrodes can be set to 0 V in a state where theelectrostatic adsorption force working between the wafer and theelectrostatic chuck electrode is set to “0”. As described above, afterthe potentials of the electrostatic chuck electrodes are set to 0 V, thewafer is released from the sample stage by the pushing-up pins, andcarried to the outside of the processing chamber by a carrying mechanism(not illustrated).

Next, the potential of the wafer during the neutralization plasma willbe described. The potential of the wafer during the neutralizationplasma is considered as equal to a floating potential during theneutralization plasma. FIGS. 5A and 5B illustrate results of measuringthe floating potential of the plasma implemented by the inventor. FIG.5A illustrates dependency of the microwave power with respect to thefloating potential, and FIG. 5B illustrates dependency of pressure withrespect to the floating potential. It can be seen from FIGS. 5A and 5Bthat the dependency of the floating potential with respect to themicrowave power and the pressure at the time of the plasma processingare not large, and the variation of the floating potential with respectto the variation of the plasma processing conditions is relatively low.The floating potential is about −15 V on the average, and −15 V becomesa potential of the wafer to be corrected. Regarding deviation in value,the absolute value of the floating potential falls within a rangebetween −12 V to −18 V, so that it is considered appropriate that themargin is −15±5 V. For this reason, ΔV of FIGS. 3A to 3D in thisembodiment is set to a value from −10 to −20 V.

Next, the description will be about a time t taken for the chargedparticles to disappear in the vacuum processing chamber after themicrowave power for generating the plasma is turned off.

The time t taken for the charged particles to disappear is a time takenuntil the charged particles generated by the plasma completely disappearfrom the vacuum processing chamber after the microwave power forgenerating the plasma is turned off as described above. However, thedisappearance of the charged particles from the vacuum processingchamber is likely to be affected not only from the state of the insideof the processing chamber such as a density of the charged particles inthe plasma and a pressure in the vacuum processing chamber, but alsofrom responsiveness of the microwave power source or the microwaveoscillation source to a control signal and a deviation of response timethereof.

A sufficient time is necessarily secured for the time t taken foreliminating the charged particles in order to exclude such an influence.On the other hand, setting the time t taken for eliminating the chargedparticles to be long does not cause a problem from the viewpoint ofneutralization. However, such an extra time taken from eliminating thecharged particles may worsen a throughput, and thus not desirable. As aresult of studying the time t taken for eliminating the chargedparticles in various conditions according to such an experiment of theinventor, 0.1 or more seconds are sufficient for eliminating the chargedparticles in the vacuum processing chamber. In addition, an upper limitof the time for eliminating the charged particles has been set to 3seconds in a range not causing a problem in throughput. In addition,since the mechanism of waiting for the elimination of the chargedparticles is similar to that of the afterglow discharge after themicrowave power is turned off, the time taken for ending the afterglowdischarge may be set to a time in a range from 0.1 to 3 seconds.

Next, an embodiment in which the inside electrostatic chuck electrode108 and the outside electrostatic chuck electrode 109 are applied withdifferent voltage at time T1 of FIGS. 3A to 3D will be described using atiming chart illustrated in FIGS. 6A to 6E focusing on configurationsdifferent from those of the embodiment of FIGS. 3A to 3D. FIG. 6Aillustrates an incident power of the microwave, FIG. 6B illustratespotentials of the electrostatic chuck electrodes, FIG. 6C illustrates anaverage value of the potentials of the electrostatic chuck electrodes,FIG. 6D illustrates the potential of the wafer, and FIG. 6E illustratesa potential difference between the electrostatic chuck electrodes andthe wafer. In addition, T0, T1, T2, T3, t, and ΔV in FIGS. 6A to 6E areused with the same symbols in FIGS. 3A to 3D and the same meaning.

In FIGS. 6A to 6E, the output voltage value of the variable DC powersource 110 on the inside is set to Va at time T1 during a period whenthe neutralization plasma is being generated, and the output voltagevalue of the variable DC power source 111 on the outside is set to Vb.At this time, an average value of Va and Vb becomes a value (that is,−ΔV in FIGS. 3A to 3D) equal to the potential of the wafer asillustrated in FIG. 6C. Since the potential difference is caused asillustrated in FIG. 6E between the inside electrostatic chuck electrodeand the wafer and between the outside electrostatic chuck electrode andthe wafer at time T1, the adsorption force between the wafer and theelectrostatic chuck electrode is not eliminated at this time.

Thereafter, the radio frequency power (microwave incident power) forgenerating the plasma is turned off at time T2. After the radiofrequency power is turned off, the charged particles in the vacuumprocessing chamber completely disappear in the predetermined time t.Thereafter, the DC voltage applied to the inside electrostatic chuckelectrode 108 and the outside electrostatic chuck electrode 109 becomes0 V at time T3. When the DC voltage applied to the electrostatic chuckelectrode becomes 0 V at time T3, an average value of the DC voltagesapplied to the inside electrostatic chuck electrode 108 and the outsideelectrostatic chuck electrode 109 varies only by +ΔV from −ΔV to 0 V asillustrated in FIG. 6C.

Since the variation in potential of the wafer is equal to the variationin average value of the DC voltages applied to the inside electrostaticchuck electrode 108 and the outside electrostatic chuck electrode 109 asexpressed in Equation 3, the wafer potential comes to vary from −ΔV to 0V at time T3 as illustrated in FIG. 6D. In other words, the potential ofthe inside electrostatic chuck electrode 108, the potential of theoutside electrostatic chuck electrode 109, and the potential of thewaver become 0 V at time T3, the potential difference between the waferand the electrostatic chuck electrode is quickly released as illustratedin FIG. 6E, and the electrostatic adsorption force working between thewafer and the electrostatic chuck electrodes disappears.

The same effects as those of the method for releasing the wafer of FIGS.3A to 3D can be obtained even by the method for releasing the waferillustrated in FIGS. 6A to 6E, and the sample can be stably releasedfrom the sample stage without causing the residual adsorption force.

Hitherto, the description has been given on the basis of the embodimentsof the invention, but the invention is not limited to these embodiments,and various changes may be made within a scope not departing from thespirit of the invention. For example, the voltage values of the DC powersource which are applied to each of the inside electrostatic chuckelectrode 108 and the outside electrostatic chuck electrode 109 areequal to each other in this embodiment, or different only in polarity.However, the voltage values of the DC power source which are applied toeach of the inside electrostatic chuck electrode 108 and the outsideelectrostatic chuck electrode 109 may be any value as long as theaverage value of both voltages becomes −ΔV. In other words, in a casewhere an average voltage of −15 V is applied as −ΔV from the variable DCpower source to the electrostatic chuck electrode, the voltage to beapplied to the inside electrostatic chuck electrode 108 may be set to −5V, and the voltage to be applied to the outside electrostatic chuckelectrode 109 is may be set to −25 V. In addition, in a case where anaverage voltage of −15 V is applied as −ΔV from the variable DC powersource to the electrostatic chuck electrode, the voltage to be appliedto the inside electrostatic chuck electrode 108 may be set to +5 V, andthe voltage to be applied to the outside electrostatic chuck electrode109 may be set to −35 V.

In addition, the control according to the invention as illustrated inFIGS. 3 and 6 is performed by the control unit 115. Further, thisembodiment has been described using the dipole electrostatic chuckelectrodes, and the invention may be applied to the monopoleelectrostatic chuck electrode.

In addition, −ΔV in this embodiment has been described as the samepotential as the wafer potential (floating potential), and −ΔV may havea value that the wafer potential at time T3 of FIGS. 3 and 6 becomesalmost “0”. In a case where −ΔV is set to the floating potential due todisturbance such as noises, the wafer potential at time T3 may become avalue not almost “0”. In a case where −ΔV is set to a value that thewafer potential at time T3 becomes almost “0”, there is an advantagethat the wafer voltage at time T3 becomes almost “0” for sure.

Hitherto, in the invention, when the sample is released from the samplestage, an average value of the voltage to be applied to theelectrostatic chuck electrodes is set to a predetermined negativepotential according to the release of the sample adsorption duringprocessing in consideration of residual charges after the plasmaprocessing for releasing the sample ends, and the voltages to be appliedto the electrostatic chuck electrodes are set to 0 V after the plasmaprocessing for releasing the sample ends. Therefore, there is no concernabout recharging after the plasma disappears. Since the potential of thewafer and the potential of the electrode both can be set to 0 V, thesample can be safely released from the sample stage without causing theresidual adsorption force.

What is claimed is:
 1. A plasma processing apparatus, comprising: aprocessing chamber in which a sample is subjected to a plasmaprocessing; a radio frequency power source which supplies radiofrequency power to generate plasma; a sample stage, which includes anelectrode to electrostatically adsorb the sample, on which the sample isplaced; a DC (Direct Current) power source which applies a DC voltage tothe electrode; and a controller configured to: change the radiofrequency power from a first radio frequency power to a second radiofrequency power after the plasma processing of the sample; change the DCvoltage from a value at the time of the plasma processing to apredetermined value while the second radio frequency power is supplied;stop the supply of the second radio frequency power while the DC voltageis being applied to the electrode at the predetermined value; change theDC voltage from the predetermined value to a value of 0V a predeterminedamount of time after the supplying of the second radio frequency poweris stopped; and release the sample subjected to the plasma processingfrom the sample stage after the DC voltage is changed to the value of0V, wherein the second radio frequency power is a radio frequency powerto generate plasma to release the sample electrostatically absorbed tothe sample stage from the sample stage, and wherein the predeterminedvalue is a value defined such that a potential of the electrodecorresponds to a potential of the sample when the DC voltage is changedto the predetermined value, and wherein the predetermined time is a timewhen an afterglow discharge disappears after the supply of the secondradio frequency power is stopped.
 2. The plasma processing apparatusaccording to claim 1, wherein the electrode includes a first electrodeand a second electrode, wherein the DC power source includes a first DCpower source which applies a first DC voltage to the first electrode anda second DC power source which applies a second DC voltage to the secondelectrode, and wherein the first DC voltage and the second DC voltageare defined such that an average value of the first DC voltage appliedto the first electrode and the second DC voltage applied to the secondelectrode is applied to each of the first electrode and the secondelectrode as the predetermined value.
 3. The plasma processing apparatusaccording to claim 1, wherein the predetermined value corresponds to afloating potential of the plasma generated by the second radio frequencypower.
 4. The plasma processing apparatus according to claim 1, whereinthe predetermined value is set to a value from −10 to −20 V.
 5. Theplasma processing apparatus according to claim 1, wherein thepredetermined amount time is a time from 0.1 to 3 seconds.